Magnetism of (LaCoO3)n+(LaTiO3)n superlattices ( n=1,2 )

${\mathrm{LaCoO}}_{3}$ provides a poignant example of a transition metal oxide where the cobalt cations display multiple spin states and spin transitions and which continues to garner substantial attention. In this work, we describe first principles studies, based on $\mathrm{DFT}+U$ theory, of superlattices containing ${\mathrm{LaCoO}}_{3}$, specifically ${({\mathrm{LaCoO}}_{3})}_{n}+{({\mathrm{LaTiO}}_{3})}_{n}$ for $n=1,2$. The superlattices show strong electron transfer from Ti to Co resulting in ${\mathrm{Co}}^{2+}$, significant structural distortions and a robust orbital polarization of the ${\mathrm{Co}}^{2+}$. We predict high-spin ${\mathrm{Co}}^{2+}$ and a checkerboard (G-type) antiferromagnetic ground state. We provide a detailed analysis of the magnetic interactions and phases in the superlattices. We predict that ferromagnetic order on the ${\mathrm{Co}}^{2+}$ can be stabilized by hole doping (e.g., replacing La by Sr), which is rather unusual for ${\mathrm{Co}}^{2+}$ cations.